1. Field of the Invention
This invention generally relates to the field of communications. More particularly, the present invention relates to a communications system that improves transmission rates and transmission distances of data signals across communications links.
2. Description of Related Art
Advances in computer capabilities as well as the unprecedented growth of Internet-related transactions have placed great demands on conventional communication infrastructures to convey data to subscribers at higher transmission rates with increased reliability and levels of service. Although conventional infrastructures communicate at higher transmission rates, such as DS-3 (e.g., 45 Mbps) and OC-3 (e.g., 155 Mbps), between networked hubs, they are generally limited in their ability to accommodate such ample bandwidths between the hubs and subscribers. Such limitations arise from the infrastructures' inability to compensate for degradations encountered on conventional transmission media spanning distances of up to 18,000 ft. between the hubs and subscribers.
Consider, for example, how common carriers provide connectivity to subscribers. Typically, carrier hubs or central offices connect to subscribers via subscriber loop circuits. Subscriber loop circuits generally comprise 2-wire transmission paths (i.e., unshielded twister pairs—UTP), which support direct current signals, low frequency (<˜200 Hz) analog signals, and voice band signals (˜200 Hz–˜3.4 KHz). These frequencies limit the transmission rate of digitally-encoded signals on the 2-wire transmission paths. Further, the longer the distances traversed by the signals on the 2-wire transmission paths, the more severe the degradation of the signals; thus, this limits the transmission rates.
To increase the transmission rates on the 2-wire transmission paths, asymmetric digital subscriber lines (ADSLs) have been developed. ADSLs combine channelization (e.g., discrete multi-tone DMT), coding (e.g., constellation/trellis encoding), and framing (e.g., super-framing) techniques to achieve upstream digital rates between 64–640 Kbps and download digital rates between 500 Kbps–7 Mbps. The ability to attain these transmission rates, however, is dependent on transmission distance. ADSLs are also sensitive to line-quality and line configurations. As a result, the higher transmission rates are available only to subscribers with “clean lines,” which are within specific distances (e.g., 8,000–10,000 ft.) from the central office. Other approaches to increase the transmission rates on the 2-wire transmission paths include line-conditioning, which increases the line-quality of a local loop. While such conditioning provides moderate improvement in transmission rates, it is line and transmission distance dependent. Accordingly, there is a need in the art for a communications system that improves transmission rates and transmission distances of data signals across communications links.